The present invention relates to an ion flow forming system.
More particularly, the present invention relates to a method and apparatus in, e.g., a plasma processing system, for attracting only positive ions from a plasma and repelling electrons and negative ions to the plasma, thereby forming a positive ion flow directed toward a target object.
Conventionally, as a plasma processing system, a plasma etching system, a plasma CVD system, a plasma ashing system, a plasma cleaning system, and the like are widely known. As such a plasma processing system (to be referred to as a plasma system hereinafter), a system, e.g., a diode parallel plate plasma enhanced system, in which a plasma generation chamber and a plasma processing chamber are integrally formed, and a system, e.g., an ECR plasma enhanced system, in which a plasma generation chamber and a plasma processing chamber are separated, are available.
In the plasma system in which the plasma generation chamber and the plasma processing chamber are separated, a mechanism that guides a plasma generated in the plasma generation chamber or charged particles (e.g., ions) in the plasma to the plasma processing chamber is required. FIG. 6 shows an ECR plasma etching system. In the ECR plasma etching system, a processing chamber 100 is formed in a hermetic processing vessel 102 which can be opened and closed. A susceptor 104 is arranged in the processing vessel 102, and a target object W (e.g., a semiconductor wafer or an LCD glass substrate) is placed on the susceptor 104 through an attraction means, e.g., an electrostatic chuck 106. The electrostatic chuck 106 is formed by mounting a plate electrode 106a between thin films made of an insulating material, e.g., a polyimide resin. When a high-voltage power is applied to the plate electrode 106a from a DC power supply 106b, the wafer W is attracted by the susceptor 104 with the Coulomb force.
The susceptor 104 is provided with a temperature adjusting means comprising a cooling unit 108, a heater 110, and the like in order to adjust the wafer W to a predetermined temperature. A heat transfer gas supply means 112 is arranged in the susceptor 104. A heat transfer gas (e.g., helium gas) is supplied to the wafer W from the lower surface through a plurality of holes in the electrostatic chuck 106, so that the heat transfer efficiency from the susceptor 104 to the wafer W is increased. An RF power supply 116 is connected to the susceptor 104 through a matching circuit 114 to apply a bias RF power to the susceptor 104.
An inlet pipe 118 for introducing a predetermined process gas (a gas mixture of, e.g., carbon fluoride gas, oxygen gas, and argon gas) into the processing chamber 100 is connected to the side wall of the upper portion of the processing vessel 102. An exhaust pipe 120 communicating with an evacuating means (not shown) is connected to the lower portion of the processing vessel 102.
A plasma generation chamber 122 for generating an ECR plasma is connected to the upper portion of the processing chamber 100. A microwave generation chamber 134 is connected to the plasma generation chamber 122 through a waveguide 130. An inlet pipe 124 for introducing a plasma generation gas (e.g., argon gas) B is connected to the upper wall of the plasma generation chamber 122. The gas in the processing chamber 100 and the plasma generation chamber 122 is exhausted by the evacuating means through the exhaust pipe 120. Predetermined process gases are introduced from the inlet pipe 118 and the inlet pipe 124 into the processing chamber 100 and the plasma generation chamber 122, respectively.
A cooling means 126 is arranged on the outer surface of the side wall of the plasma generation chamber 122, and heat generated in the plasma generation chamber 122 is radiated. A magnetic coil 128 is arranged outside the cooling means 126 to surround the plasma generation chamber 122.
The plasma generation chamber 122 is connected to the microwave generation chamber 134 through the waveguide 130 that propagates the microwave. A microwave (e.g., a 2.45-GHz microwave) oscillated by the magnetron (not shown) of the microwave generation chamber 134 propagates to the plasma generation chamber 122 through the waveguide 130 and an insulating wall 132. Electric discharge is excited in the plasma generation chamber 122 by the propagating microwave. A magnetic field of, e.g., 875 Gauss, is applied to the interior of the plasma generation chamber 122 by the magnetic coil 128. During electric discharge, the electrons perform cyclotron motion to generate the ECR plasma for the plasma generation gas B.
Since the predetermined process gas A is introduced into the processing chamber 100, the reactive gas in the process gas is dissociated due to the function of the plasma (electrons) generated in the plasma generation chamber 122, to generate radicals.
A bias RF power is applied from the RF power supply 116 to the susceptor 104 in the processing chamber 100 through the matching circuit 114, and the interior of the processing chamber 100 is evacuated through the exhaust pipe 120. Therefore, the plasma and radicals generated in the plasma generation chamber 122 are guided onto the susceptor 104. A target film (e.g., a silicon oxide film) on the wafer W placed on the susceptor 104 is etched by the plasma and radicals.
This ECR plasma processing system is more suitable to advanced micropatterning of a target object than the conventional diode parallel plate plasma enhanced system and the like. The ECR plasma processing system can easily control etching shape ranging from anisotropic etching to complete isotropic etching. Also, since the ionization rate is high, high-speed etching with less damage can be performed with a low ion energy. Furthermore, since no-electrode discharge is utilized in the processing chamber 100, contamination is few.
In such a plasma processing system in which the plasma generation chamber and the plasma processing chamber are separated, the ions in the plasma generated in the plasma generation chamber must be efficiently attracted into the processing chamber in order to increase the plasma processing efficiency. In the system shown in FIG. 6, however, not only ions necessary for plasma processing but also electrons are diffused and attracted from the plasma generation chamber simultaneously, and are introduced to the processing target in the plasma processing chamber.
Since a force that maintains the electrical neutral state acts between the ions and electrons, it is very difficult to separate the ions and electrons and to introduce only the ions into the processing chamber efficiently. When the electrons and ions (charged particles) are mixed, it is not easy to control only the charged particles with a mechanism combined with an electrode. The advantage of separating only the ions from the plasma arises from this respect. In the plasma ion source, to separate and extract only the ions from the plasma is a prerequisite. In plasma CVD, high-energy injected ions also have an advantage of making the film dense. Inversely, however, if the ion energy is excessively high or the number of ions is excessively large, the ions largely damage the film, which is a disadvantage. In another point of view, ions also have an effect of increasing the film deposition rate (ion induced deposition). When the effect of ion etching is excessively large, an underlying different film is also etched to cause contamination. In any case, to control the injecting ion energy is significant. In the ion source, to control the injecting ion energy is indispensable, as a matter of course.
Furthermore, in the system shown in FIG. 6, it is difficult to control ions mixed with electrons to a desired state, i.e., to cause them to be injected in a desired direction. Therefore, various types of ion flow control means such as an electric field generating means for generating a predetermined electric field in the plasma processing chamber are required.